Lessing understated the case for Aw's debut novel. It was not merely unputdownable, but moving, stylish, true and disturbingly haunting – a mature piece of work for a writer then barely into his thirties. The book deservedly won a clutch of prestigious prizes and was listed for the Man Booker – an almost impossible act to follow.

Now, four years later, comes Aw's attempt at a worthy successor. And it's buoyant, limber, confidently told – and cleverly carries within its pages both the substance and momentum of a sequel. Yet, long before its cliffhanger ending, what is revealed is a book embodying huge ambition, jostling with love, betrayal and guilt, all set poignantly and subtly against the politics of turmoil in post-colonial Indonesia circa 1964.

At the story's heart are two young brothers abandoned early to an orphanage, then adopted by different families. Johan, the 13-year-old, is taken to Kuala Lumpur and grows up rich, an angry wild child, indulged by his new "mother" but irked by the strictures of his "father". Adam, the five-year-old younger brother, becomes the foster-son of Karl, a quiet Dutch painter who sees Indonesia as his true home.

Johan feels guilty at having betrayed his brother's trust. Adam nurtures the pain of their separation while remembering little of orphanage life, and asks Karl to fill in the blanks. Karl pleads ignorance. Adam suspects that he is lying.

Map of the Invisible World (the title is a reference to the children's early life), is, among other things, a quest tale, a search for solace, and for belonging and brotherly love. And yet it starts with a terrible jolt, a further blow of separation, with Karl's abduction (snatched by the Indonesian army from the island he shares with Adam – he is the victim of a programme of "ethnic cleansing" by the regime), while Adam, now 16, watches from the shadows, again bereft. The novel pursues his attempt to find Karl and secure his release. Among Karl's possessions he finds old photographs of Margaret, Karl's former lover, who is now a lecturer in Jakarta. Margaret becomes the story's lynchpin. It is through her that Adam finds Din, her tutor-assistant. Din promises Adam he'll help find Johan. A double pursuit now seems in the offing.

Din is brilliantly portrayed, a double-deceiver who leads the story into the shadows of revolution. Margaret symbolises hope – she has never abandoned her love of Karl. And with Adam's appearance she finds new energy to pursue the unfinished business of their affair. Meanwhile Johan, far away, detached from the centre of the narrative, seems like a figure hatched from a dream, bruising and brutalised by turns.

As in his debut novel, Aw, by degrees, immerses himself in his characters' tangled lives and the questions they raise. He begins more slowly this time, obliquely revealing plot points like a miser counting out heartbeats of suspense. Will the brothers find each other? Will Margaret and Karl find fulfilment? Will Karl be found dead? And what, above all, of the street-level violence (nicely blending the pace of fiction with the detail of documentary), that threatens Adam's continuing tortuous quest?

Stalking both brothers is the spectre of the other life – "the real life". "Do you ever feel," asks Johan, talking to his younger adoptive sister, "that your real life is somewhere else, that someone has stolen it and taken it to another place far away …?" This raises obliquely the question of home and how to define it, another gnawing, stewing, fundamental matter that hobbles both Margaret and Karl to degrees, but which for Din is irrefutable and fixed. He knows who he is.

The novel's tensions lie in that no-man's-land between fixity and uncertainty. Aw explores it, without ever falling into abstractions. For his is a story about the ties of human love, those that defy human separation. Yet another kind of invisible world.